This invention relates to window panels of the type used for aircraft windshields. In order to meet the service requirements of modern high speed aircraft, the window panels must withstand thermal and pressurization loads and provide clear undistorted vision to the pilot. Provision also is required for mounting of the window panels on the aircraft structure to evenly transfer the service loads from the panels to the structure. In many cases, it is desired to bend the panels into complex curved configurations to conform to the aircraft structure. It is very difficult to form the curved panels so that the peripheral edges precisely fit or match the contour of the mounting surfaces of the frame openings. This has resulted in residual stresses being imposed on the panels due to forced matching of the misfit panels to the mounting surfaces and/or has also required unmatched mounting and potting of the voids between the mounting surfaces and the panels. As a result, heavier panels of greater strength have been required because the ultimate strength of a panel is reduced by the residual stresses from forced matched mounting of the panels and/or because the glass will be unevenly stressed in tension loading in the case of unmatched mounting.
Window panels of the general type for which the present invention may be adapted are disclosed in U.S. Letters Pats. Nos. 3,356,833, 3,410,739, 3,424,642, 3,414,445, and 3,616,122, granted to Dee R. Orcutt. Although these patents show and describe window panels and methods for making the panels providing a superior product, they assume an exact shaping of the panels and a precise fit of the panel edges with a minimum provision for variability in fit between the panel edges and the mounting surfaces. As stated above, variability in fit may cause excessive strains on the transparent sheet where the fit is not precise. There may also be residual stresses developed in the transparent sheet by the forced attachment of the panel to the mounting surface. These problems are further compounded by the stress induced by temperature differentials to which the window panels are subjected which may range from -65.degree. F. to +180.degree. F. Also, the window panels must generally be adaptable for heating by suitable means such as a transparent electrical conductive coating or by fine resistance wires embedded in an interlayer of the panel. Such heating for deicing and defogging purposes may be a further source of imposing stress on the transparent panel.